Silver chlorobromide containing substantially no silver iodide is used for expediting the development speed of products used in the market where there is a great demand to finish a large amount of prints in a very short period of time as in photographic materials for color photographic paper.
The demand for improving rapid processing of color photographic paper has increased more and more in recent years, and there have been made many studies directed to the improvement thereof. For example, it is well known that when the silver chloride content of silver halide emulsions used is increased, the development speed can be greatly improved.
Further, it is conventionally well known that sensitizing dyes are added to silver halide emulsions to enlarge the sensitive wavelength regions of the silver halide emulsions and to optically sensitize the emulsions in the preparation of silver halide photographic materials.
Many compounds, conventionally referred to as spectral sensitizing dyes, are used for this purpose. Examples of spectral sensitizing dyes conventionally used include cyanine dyes, merocyanine dyes and xanthene dyes described in T. H. James, The Theory of the Photographic Process, third edition, pp. 198 to 228 (Macmillan, N. Y., 1966). It is also known that these dyes may be used either alone or in combination (e.g., for the purpose of supersensitization).
Generally, when these sensitizing dyes are applied to silver halide emulsions, only the sensitive wavelength regions of the silver halide emulsions are enlarged, but the following conditions must also be met.
(1) The material is spectrally sensitized to the proper region.
(2) Sensitizing efficiency is good, and sufficiently high sensitivity can be obtained.
(3) Fogging is not caused.
(4) The difference in photographic performance caused by the difference between lots (i.e., variability from lot to lot) in the preparation of silver halide photographic emulsions is small.
(5) Unevenness in sensitivity due to change in temperature during exposure is small.
(6) There is no adverse interaction of the dyes with other additives such as stabilizers, anti-fogging agents, coating aids, color formers, etc.
(7) A lowering in sensitivity is not caused when silver halide emulsions containing sensitizing dyes are stored, particularly under high temperature and humidity conditions.
(8) Color turbidity (color stain) is not caused by diffusing the added sensitizing dyes in other light-sensitive layers after development.
The above-described conditions are important factors in the preparation of silver halide emulsions, particularly for silver halide color photographic materials.
Supersensitization is described in Photographic Science and Engineering, Vol. 13, pp. 13 to 17 (1969), ibid., Vol. 18, pp. 418 to 430 (1974) and James, The Theory of the Photographic Process, 4th Edition, p. 259 (Macmillan, 1977). It is known that high sensitivity can be obtained by choosing suitable sensitizing dyes and supersensitizing agents.
However, when using silver halide emulsions having a high silver chloride content (namely, high silver chloride emulsion) which have increasingly been in demand lately in the photographic market as described above, there is much difficulty in obtaining sensitizing dyes which satisfactorily meet the above-described requirements which can be fulfilled by emulsions mainly composed of silver bromide.
Thus the difficulty in obtaining high silver chloride emulsions which have high sensitivity and sufficiently high storage stability and are low in variability from lot to lot is a very important problem to be solved.
Attempts have been conventionally made (1) to improve the spectral sensitivity or preservability with time of silver halide emulsions containing silver chloride which is spectrally sensitized with spectral sensitizing dyes or (2) to prevent the emulsions from being fogged by infrared rays. For example, JP-B-4610473 (the term "JP-B" as used herein means an "examined Japanese Patent publication") and JP-B-48-42494 propose the addition of nitrogen-containing compounds, JP-A-505035 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") proposes the addition of supersensitizing agents, JP-A-52-151026 proposes the addition of water-soluble bromides, JP-A-54-23520 proposes the addition of iridium and JP-A-60-202436 proposes the addition of hardening agents. Further, JP-A-58-7629 discloses an improved method for adding spectral sensitizing dyes, and JP-A-60-225147 proposes the use of silver chlorobromide having (100) face and (111) face.
It is conventionally known that pentamethinecyanine compounds in which the 2- and 4-positions o the methine chain are crosslinked with a trimethylene group, are superior in sensitivity and storage stability. For example, these compounds are described in JP-A-60202436, JP-A-60-220339, JP-A-60-225147, JP-A-61-123834, JP-A-62-87953, JP-A-63-264743, JP-A-1-155334, JP-A-1177533, JP-A-1-198743, JP-A-1-216342, JP-A-2-42, JP-B-60-57583 and U.S. Pat. No. 4,618,570.
However, these patent specifications disclose only dyes in which the 2- and 4-positions on the methine chain are crosslinked with 2,2'-dimethyltrimethylene group as in the following dye A. ##STR2##
Further, dyes in which the 2- and 4-positions on the methine chain are crosslinked with an unsubstituted trimethylene group, are disclosed in U.S. Pat. No. 2,481,022.
Furthermore, dyes in which a trimethylene crosslinking group substituted by an alkyl or aryl group on the 2-position is positioned at the 2- and 4-positions on the methine chain, are disclosed in U.K. Patents 595,783, 595,784, 595,785 and 604 2,481,022 and 2,756,227, Kanko Kagaku Yoko Kagaku, page 39 (1987) (written in Japanese), and Journal of Imaging Science, 32, page 81 (1988).
With regard to photographic performance as silver halide photographic material, however, the above references have only limited disclosures. Thus, U.S. Pat. No. 2,481,022 discloses that silver iodobromide is spectral-sensitized; Journal of Imaging Science, 32, page 81 (1988) discloses that silver bromide is spectral-sensitized; and Kanko Kagaku Yoko Kagaku, page 39 (1987) discloses that silver chlorobromide is spectral-sensitized.